The present invention relates to antennas and more particularly to a device to be attached to an omni-directional antenna having an elongated conductive element to improve the transmission and reception.
While the discussion of the device of the present invention will be in relation to antennas for citizens band radio antennas for simplicity, it is to be understood that it has application to antennas employed for other frequencies.
Vertical antennas are frequently employed on both land and water mobile vehicles for both transmitting and receiving communications. Most mobile antennas for citizens band radios, for example, are omni-directional and are formed of an elongated conductive element adapted to be mounted vertically. Such antennas are generally constructed of a metallic tube or rod having an electrical length equal to a quarter-wave in length of the desired communication frequency. These range in physical length from about nine feet for 27 MHz to about six inches for 470 MHz. The antenna length may be physically lengthened or shortened to accomodate waves of various frequencies. When this is not practical the antenna is loaded by adding inductance to increase its effective length or by adding capacitance to decrease its effective length. Another type of verticle antenna in use having an elongated conductive element is a helical antenna which consists of an insulating post such as fiberglass and an antenna conductor, such as copper wire, which is wound helically about the post to define the helical antenna.
For motor vehicles, the antennas are generally physically smaller than that required for maximum efficiency and are provided with a loading coil in an effort to compensate for the shortening of the antenna. These antennas have a range less than that desired.
It is therefore the desire of this invention to provide a device which will improve the range of transmission and reception of an omni-directional antenna of the type having an elongated conductive element adapted to be mounted generally vertically.
It is also desirable to provide such a devise for improving the transmission and reception of such types of antennas which can be easily mounted on the existing antenna without modification and is particularly suitable for mobile antennas.
It is also desirable to provide such a device for attachment to such types of antennas which will reduce the static received at the designated frequency.